CONDITIONS OF CHEMICAL CHANGE 83 



elusion was drawn that ozone produced in the path of the 

 electric discharge results from the action of ultraviolet light 

 and cathode rays on oxygen, a view which received further 

 support from the circumstance that the amount of ozone formed 

 in a given time was roughly proportional to the intensity of 

 the light. 



E. Warburg and E. Regener l were the first to demonstrate 

 that ultraviolet light could induce other chemical changes 

 besides the conversion of oxygen into ozone. As a source of 

 ultraviolet light they employed an electric spark between 

 aluminium electrodes. With their apparatus 2'2 per cent, of 

 oxygen at atmospheric pressure could be converted into ozone. 

 They found that ammonia, nitric oxide and nitrous oxide were 

 readily decomposed by the light. 



S. Chadwick and J. E. Ramsbottom and the writer have 

 shown that the ultraviolet light emitted by a quartz mercury 

 lamp will bring about the interaction of oxygen and hydrogen 

 or carbon monoxide and effect the decomposition of carbon 

 dioxide into carbon monoxide and oxygen. As might be ex- 

 pected, the presence of moisture has a very marked effect 

 both on the union of carbon monoxide and oxygen and on 

 the decomposition of carbon dioxide. Its accelerative influence 

 on the one change, the combination of the carbon monoxide 

 and oxygen, is so much greater than that on the reverse 

 change, the decomposition of carbon dioxide, that although 

 dry carbon dioxide is decomposed to the extent of 46 per cent, 

 at a low pressure by ultraviolet light, it is scarcely affected 

 by the same agency when it contains moisture. When a 

 carefully desiccated mixture of carbon monoxide and oxygen 

 and a similar mixture in a moist condition are submitted to 

 the action of ultraviolet light of the same intensity, the rate 

 of contraction is the same in both cases ; but the contraction 

 in the first case is due mainly to the formation of ozone, 

 whereas in the second it is caused principally by the pro- 

 duction of carbon dioxide. A. Holt 2 has obtained very similar 

 results by decomposing carbon dioxide at a low pressure by 

 the silent discharge ; but at a higher pressure the results he 

 obtained were different from those furnished by our experi- 

 ments with ultraviolet light. He believed that the chemical 



1 Sitzungsber. K. Akad. Wiss. Berlin, 1904, 1228. 

 * Trans. Chem. Soc. 1909, 95, 34. 



